<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			.aaa{
				width:1000px;
				height: 500px;
				background: green;
				margin: auto;
			}
			
/*calc  设置盒子宽高，内容区+外边距，不包括内边距和盒子
 		运算符两边要用空格分开*********************************************/			
			.bbb{
				width: calc(25% - 20px);
				height: 300px;
				background: red;
				float: left;
				margin: 10px;
			}
			
			
			
		</style>
	</head>
	<body>
		<div class="aaa">
			<div class="bbb">
				<div class="ccc"></div>
			</div>
			<div class="bbb">
				<div class="ccc"></div>
				
			</div>
			<div class="bbb">
				<div class="ccc"></div>
				
			</div>
			<div class="bbb">
				<div class="ccc"></div>
				
			</div>
		</div>
		
		
	</body>
</html>
